The use of hydrous oxide ion exchangers, including both anion and cation exchangers, as adsorbents for separating inorganic ions from solution is disclosed in U.S. Pat. Nos. 3,332,737 and 3,382,034. The patentee points out certain advantages of the materials disclosed and claimed over the prior art adsorbents or ion exchangers such as silicates, clays, zeolites, and organic resinous exchangers, etc. Such advantages include improved stability to acids, bases, oxidizing and reducing agents, temperature, and radiation from radioactive ions. The patentee further points out that ferric oxide has been used as an inorganic absorbent. However, it is noted that ferric oxide is in a class of inorganic adsorbents having low ion capacity and/or low selectivity. In the U.S. Pat. No. 3,382,034 it is disclosed that Group VI hydrous oxide ion exchangers may be used to remove anions such as chrominum, molybdenum and tungsten. Although ferric oxide is mentioned in both of these patents as an adsorbent there is no teaching that ferric oxide may be used to remove the molybdenum or tungsten anions noted above.
U.S. Pat. No. 3,476,553 discloses a process for recovering metals from metal-containing solutions by precipitating the metals as insoluble metal hydroxide floccules or insoluble basic salts or hydroxides. The metal-containing, insoluble hydroxides or salts are subsequently collected by contacting with a surface-active collector that is ionically charged. The surface-active collector is adsorbed at the surface of the metal-containing, insoluble hydroxide or salts to form a complex and the complex is removed by bubbling gas throughout the solution to buoy the complex and allow it to rise to the surface.
U.S. Pat. No. 3,804,945 discloses the use of gels for extracting metal values from solution by passing the solution through a column of dehydrated gel. Although ferric oxide is disclosed as a suitable gel, there is no disclosure that it can be used to remove tungsten values from solution.
U.S. Pat. No. 3,931,007 discloses the treating of waste waters with iron compounds such as .alpha.-FeOOH, .gamma.-FeOOH, and Fe.sub.3 O.sub.4 to remove dissolved heavy metals. This reference does not teach the extraction of tungsten or molybdenum and in addition, the iron compounds are formed in situ.
Processes for separating tungsten and molybdenum values from solution are known in the art. For example, U.S. Pat. No. 1,292,559 (to Andersen) discloses a process for separating tungsten compounds from, e.g., "an alkaline solution of tungstic aacid." In the process, ferric sulfate may be added to complex with the tungstic ions. The U.S. Pat. No. 2,962,349 (to Anglin) discloses a method of recovering tungstates from dilute solutions thereof by precipitation with, for example, a water soluble salt of iron.
U.S. Pat. No. 3,510,273 (to Fitzhugh et al) discloses a method for the recovery of molybdenum from aqueous solutions thereof by the addition of metallic iron. U.S. Pat. No. 3,758,665 (to Vojkovic) discloses a method of recovery of metals including tungsten and molybdenum from aqueous solutions thereof by precipitation with a ferric salt. None of these patents, however, make any direct reference to the use of iron hydroxyoxides as an inorganic adsorbent for the recovery of such tungsten or molybdenum values.
Many workers have studied the preparation of various iron oxides and hydroxides by precipitation from aqueous solutions. See, for example, G. Brauer, "Handbook of Preparative Inorganic Chemistry," Volume 2, 2nd Edition, Academic Press (1965) New York. It will be noted that such workers did not isolate the preferred hydrous oxide of iron claimed hereinbelow, nor did such worker utilize iron oxides or hydroxides for the extraction of molybdenum and/or tungsten from solution.